1. Field of the Invention
The present invention relates to a headrest of an automotive seat, and particularly to a structure of a powered headrest of a vertically movable type which is provided on the top of seat back of the seat and operable by a motor to raise or lower the headrest body.
2. Description of Prior Art
Typically, a headrest is provided via a pair of stays upon the seat back of an automotive seat or the like. Also known is a powered headrest of a vertically movable type wherein the headrest body may be moved under a motor drive control in a vertical direction relative to the seat back. Basically, its structure uses normally a DC geared motor and a motor drive control system based on a switch operation, thus enabling a user to adjust the headrest body to an optimum height for his or her head position by operation of switches.
In this sort of powered headrest, best known is the one of type wherein a motor is mounted within the headrest body. This has however involved such problem that the weight of headrest body is increased due to its having a motor therein, and the motor is not easy to be installed in the small inner space of headrest body. The outcome will be that the increased weight of headrest body means an increase of inert force in fore-and-aft direction in such a case of collision, which will deform and break the securing portion of motor and headrest stays, and that the installation of motor in the small space of headrest body makes more complicated the inside structure of the headrest body and requires troublesome steps of installing the motor therein, resulting in an obstacle for speed-up in the assemblage.
To address such problem, there has been known a headrest structure wherein the motor is installed in the seat back and operatively connected to the headrest body through a suitable mechanism which is arranged in both seat back and headrest body.
Yet, when it comes to the application of this vertically movable headrest structure to a fore-and-aft movable headrest mechanism, another problem arises in the complexity of mechanic elements in the seat back. That is, in the fore-and-aft movable headrest mechanism, a shaft is rotatably journalled within the seat back and rotated by a drive mechanism in the forward and backward directions, and upon that shaft, the headrest stays are fixed, so that the headrest body may be rotated forwardly and backwardly relative to the seat back. Its purpose is for providing a vision field widening effect; namely, when the headrest is rotated forwardly down to a headrest non-use position at the seat back, an occupant on the other seat can widen his or her vision field at the upper end of seat back where the headrest has been rotated at the non-use position. However, this ordinary conventional arrangement will make greater the scale of associated mechanic elements and make more complicated their mechanisms, thus resulting in posing a technical difficulty in materializing the forward and backward motions in the present vertically-movable powered headrest structure.